1. Field of the Invention
The present invention relates to an apparatus for controlling a sheet supplying device for introducing sheets stacked in a cassette into a predetermined conveyance path and preventing the supplying of a sheet which must not be fed in the case where a multiplicity of sheets are simultaneously fed.
2. Description of the Related Art
The inventors of the present invention know copying machines which have been arranged such that a plurality of sheet cassettes are provided in a desk disposed below the copying machine body so that copying sheets of various sizes are accommodated depending upon the desired sheet supplying directions. Thus, a desired copying sheet is selected so as to easily change the copying sheet as much as possible (refer to Japanese Patent Laid-Open No. 61-192637).
The copying machine of the type described above has a sheet supplying device for supplying the copying sheets stacked in a sheet cassette to the sheet conveyance path, and the sheet supplying device is disposed above the sheet supplying side of the sheet cassette. Although the sheet supplying device of this type is arranged to supply the copying sheets one by one, two sheets may be simultaneously and undesirably fed (double feed) since the copying sheets are sticked together due to static electricity.
Accordingly, the sheet supplying devices having a device for overcoming the above-described problem has been invented by many inventors. For example, a known device which has been disclosed in Japanese Patent Laid-Open No. 53-129648 for preventing the double feed. That device has a pad so arranged that it can be brought into contact with a roller and separated from the roller, and the frictional coefficient of the pad is made smaller than that of the roller.
However, according to the above-described sheet supplying device, the conveyance of only the lower copying sheet of the two copying sheets is prevented for the purpose of preventing the double feed. Therefore, the copying sheet is sometimes left with projecting over the cassette even if the pad is separated from the roller. As a result, when the cassette is drawn from the desk for feeding the copying sheets or eliminating the jamming of the copying sheets, the copying sheet left as described above comes in contact with the sheet supplying device and is damaged.
In particular, in the case where the above-described sheet cassette is a rotatable sheet cassette with which the copying sheets can be supplied either longitudinally or sideways, the sheet is rotated for the purpose of changing the supplying direction. Therefore, the copying sheet can be easily damaged, causing a difficulty in supplying the copying sheet.
It might therefore be feasible to employ a structure arranged such that a sheet returning plate is provided therein, and the sheet returning plate pushes the leading edge of the copying sheet for preventing the supplying of the copying sheet on the tangent line between the sheet supplying roller and the pad so as to return the copying sheet to the sheet cassette.
However, even if the sheet returning plate of this type is provided, the sheet returning plate cannot reach the leading edge of the copying sheet and the sheet returning operation cannot thereby be conducted in the case where the leading edge of the copying sheet which must not be fed exceeds the roller tangent line and is stopped there. For example, if three copying sheets have been simultaneously fed (triple feed), the upper copying sheet is fed by the sheet supplying roller and the supplying of the lower copying sheet is prevented by preventing device such as a pad. However, the intermediate copying sheet is conveyed together with the upper copying sheet, and is stopped at a position exceeding the roller tangent line.